<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

    <form action="/calc">
        <input type="number" name="numA" th:value="${obj.numA}">
        <select name="operator">
            <option value="1">＋</option>
            <option value="2">－</option>
            <option value="3">×</option>
            <option value="4">÷</option>
        </select>
        <span th:text="${obj.operator}"></span>
        <input type="number" name="numB" th:value="${obj.numB}">
        =
        <input type="number" th:value="${obj.result}" />

        <br />
        <input type="submit" value="计算" />
    </form>

</body>
</html>